The present invention relates to a method for operating an internal combustion engine, with which the pressure in suction portion is determined from the position of a throttle flap, a signal produced from the position of the throttle flap is passed through at least one delay element and the passed signal is used for forming a limit for a permissible value region.
Such a method is known. In the method the angle of a throttle flap which is taken by a sensor is stored in a low pass filter. A maximal and a minimal value is formed from the filtered and the unfiltered signal, from which an upper limit and a lower limit for a permissible pressure region is determined. Simultaneously the pressure is detected by a sensor. This is performed so that the pressure is read over a segment (time between two ignitions) per 1 ms and added. Then a pressure determination is performed, in that the added value is divided by the number of the tests (arithmetical average value formation). If the pressure detected by the sensor is located outside of the permissible value region, an input in an error storage is performed. Moreover instead of the pressure value detected by the pressure sensor, the pressure value determined from the angle of the throttle flap is used for calculation of filling of a combustion chamber of the internal combustion engine. Thereby a second pressure signal is modeled, which is suitable for monitoring (diagnosing) of the measured pressure signal of the sensor.
The basis of the diagnosis method is therefore the determination of the suction pipe pressure from two different ways. On the one hand the suction pressure is determined directly by a sensor. The thusly obtained value is used for determination of the air filling in a combustion chamber. On the other hand a corresponding pressure is determined from the angle of the throttle flap and the rotary speed. In the case of a deviation of a pressure, a faulty pressure sensor is at issue. Since during a fast change of the angle of the throttle flap due to the compressibility of the air and the suction pipe time constants the actual pressure changes only with a low speed, the signal produced by the throttle flap must be delayed. This is performed by the low pass filter.
It has been however determined that there are situations in which an input in the error storage is performed, while the pressure sensor operates obviously correctly. Such an error recognition of a faulty operating pressure sensor can for example take place when the throttle flap is moved highly dynamically. In this condition for example a very fast opening and an immediately following fast closing of the throttle flap is produced.
Accordingly, it is an object of the present invention to provide a method of the above mentioned general type which avoids the disadvantages of the prior art.
More particularly it is an object of the present invention to provide a method of the above mentioned type, which excludes the above mentioned faulty detection.
In keeping with these objects and with others which will become apparent hereinafter, one feature of present invention resides, briefly stated, in a method in accordance with which two delay elements are provided, wherein the delay of one delay element is switched off when the speed of changing the position of the throttle flap is located above a positive limiting value and the delay of the other delay element is switched of when the speed of changing and the position of the throttle valve flap is located under a negative limiting value.
In accordance with the present invention it has been determined that the faulty detection or in other words the faulty response of the diagnosis while the pressure sensor is in order is caused in the prior art because at high movement speed of the throttle flap and an abrupt direction change of the movement of the throttle flap, the time for the delay element is too short to swing to a target value. During such a direction change of the movement of the throttle flap, a sign change of the movement speed of the throttle flap is performed, or the so-called throttle flap gradient. When the sign change is performed at a time point at which the low pass filter did not swing to its target value resulting from the opening movement of the throttle flap, a permissible value region is obtained which is located under the actual pressure acting in the suction portion and detected by the pressure sensor. For better understanding such process is illustrated in FIG. 4.
This problem is resolved in the present invention in that, the two delay elements are provided. In the case of a high speed of the throttle flap, the delay of one of the both delay elements is switched off. This means that the stored signal passes through the delay element with a delay, the output signal of the delay element is equal to the input signal. When the movement speed of the throttle flap is again outside the high dynamic region, or in other words under the limiting speed, a normal delay of the signal is performed by the delay element. With this features, in the case of high movement speeds of the throttle flap no delayed swinging of the delay element to a target value is performed, but instead the output signal of the delay element is directly coupled to the input value. During following movement of the throttle flap in an opposite direction, also with a correspondingly higher speed or dynamic of the throttle flap, the short-time switched off delay element remains active and delays the input signal correspondingly, while as a start value for the delay, the signal which is reached during the switched-off delay is utilized.
In accordance with the present invention in the event of a fast opening movement in the throttle flap, one delay element is inactive, while to the contrary the other delay element is active. In the case of a fast closing movement of the throttle flap the one delay element is active, while to the contrary the other delay element is inactive.
In the inventive method it is guaranteed with the signals which pass through both delay elements, a permissible value region can be formed, which with the correctly operating pressure sensor corresponds to actually permissible region.
In accordance with a further embodiment of the present invention, the delay element includes at least one low pass filter. With such low pass filter, a delay element can be realized with a software in a simple way. It is also possible to form the delay element for example as a controller, in particular PI controller.
It can be further provided that the both limiting values have the same amount and differ by the signs. This is provided especially when the fluid conditions are such that the characteristics during the pressure increase and the pressure decrease in each region of the suction portion in which the pressure sensor is arranged, do not substantially differ from one another.
In accordance with a further embodiment of the present invention, at least one characteristic field is provided, with which from the rotary speed of the internal combustion engine and from the signal produced from the position of the throttle flap, the corresponding pressure is determined in the suction portion. With such a characteristic field, there is a simple feature to realize, with which the relatively precise value for the pressure in the suction portion can be determined. The characteristic field can be arranged before the delay elements as seen in a signal flow direction. In another case, the signals passing through the delay elements are each stored in its own characteristic field.
It is especially advantageous when the pressure in the suction portion is measured and compared with the permissible value region. Thereby a diagnosis of the measuring device is possible, which measures the pressure in the suction portion.
An error command and/or an input in an error storage is performed for example when the measured pressure is located outside the permissible value region. In this way the user and/or a person who performs a maintenance becomes aware of a faulty pressure sensor.
In addition or alternatively it can be provided that when the measured pressure is located outside the permissible value region, the determination of the filling of a combustion chamber of the internal combustion engine is performed on the basis of the signal produced from the position of the throttle flap. If the measured pressure is located outside of the permissible value region, it can be determined that the pressure sensor operates in a faulty manner. The pressure sensor is however conventionally provided for the determination of the filling of the combustion chamber. When the pressure sensor is diagnosed as faulty, the less accurate, but reliable operation of determination of the air filling can be determined from the position of the throttle valve.
The present invention deals also with a computer program, with which the performance of the above mentioned method is possible, when it is carried out on a computer. It is especially advantageous when the computer program is stored on a storage, in particular a flash memory.
The present invention also deals with a control and/or regulating device for operating an internal combustion engine. With the use of this device, in connection with the above mentioned method, the advantages are obtained which are specified herein above, when the control and/or regulating device is suitable for controlling and/or regulation of the above mentioned method.
The novel features which are considered as characteristic for the present invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.